Free-piston-type engine



April 13, 1961 A. H. MULLER 2,980,086

FREE-PISTON-TYPE ENGINE Filed June 11, 1959 INVENTOR.

ALFRED H. MULLER FREE-PISTON-TYPE ENGINE I Alfred H. Miiller, Waiblingen, Germany, assignor to Daimler-Benz Aktiengesellschaft, Stuttgart, Germany Filed June 11, 1959, Ser. No. 819,694 I Claims priority, application Germany June 11, 1958 6 Claims. (Cl. 123-46) The present invention relates to improvements in a free-piston-type engine which consists of at least two piston units which Work in opposite directions and are disposed coaxially to each other in the longitudinal direc tion of the engine, and wherein each piston unit comprises grally connected to a combustion piston, thus forming a three-piston unit, and each combustion piston of one unit operates in the opposite direction to the combustion piston of an adjacent unit and within a combustion chamber which is common to both units.

There have also been prior proposals of free-pistontype engines consisting of several coaxial engine units in which each compressor piston is likewise connected at each side thereof to a combustion piston, but in which the central adjacent combustion pistons do not have a common combustion chamber but each combustion piston is associated with a separate cylinder head and combustion chamber. Also, all of the combustion pistons have the same diameter.

It is an object of the present invention to provide a free-piston-type engine of the above-mentioned kind anhich has the advantage over similar engines as previously known that it may be manufactured at a very low expense and produces a much higher output, for example, when used as a generator of propellent gases which are intended for operating a combustion turbine which is connected thereto.

For attaining this object, the present invention provides that the two inner combustion pistons operate within a common combustion chamber according to the uniflowscavening method, while the outer combustion pistons operate according to the reverse or loop scavenging method, and that the sides of two air-compressor pistons facing toward the outer combustion pistons supply the common central combustion chamber with compressed air, while the sides of the air-compressor pistons facing toward the counteracting combustion pistons supply the two outer combustion chambers with compressed air.

It is a fact well-known in the art that, insofar, as the engine efficiency is concerned, the uniflow-method of scavenging is far superior to any other scavenging method, for example, the reverse-scavenging method, since it results in a higher mean pressure, particularly because of the higher volumetric efliciency attainable.

In connection with several coaxial piston units of a United States PatentO Patented Apr. 18, 19,61

2. free-piston-type engine as above described, which are provided according to the invention with individually operating outer combustion pistons with reverse or loop scavenging and inner, counteracting combustion pistons with uniflow scavenging, it is a further object of the present invention to attain a substantially equal output or a substantially equal volume of propellent gases with both groups of combustion pistons, that is, the group operating according to the uniflow-method of scavenging and the group operating according to the reverse-method of scavenging, so that a more uniform current of propellent gases will be attained insofar as the volume and the .energy thereof is concerned, which is of the greatest importance for the manner of operation of a combustion turbine to which these gases are supplied.

For attaining this object, the present invention further provides that each pair of combustion pistons, which are associated with two different compressor pistons and operate with uniflow scavenging in opposite directions to each other and have a common combustion chamber, is made of a smaller diameter than the diameter of the two other outer combustion pistons which operate with reverse scavenging, so that the sides of two air-compressor pistons facing toward the outer combustion pistons supply the common central combustion chamber with compressed air, while the sides of the air-compressor pistons facing toward the inner counteracting combustion pistons supply the two outer combustion chambers with compressed air.

This feature of the present invention results in several important advantages. Since the sides of the air-compressor pistons, which together with the cylinder have a greater piston displacement than the other sides of the air-compressor pistons, supply compressed air to the combustion chambers which operate with reverse scavenging, the volume and energy of the propellent gases produced will be more uniform in all combustion cylinders. Furthermore, the substantially uniform output of the various operation of the inner pistons in opposite directions to occur according to the more efficient uniflow-method of scavenging, and that both methods may be applied in the same engine unit without causing any disadvantages.

These and other objects, features, and advantages of the present invention will become further apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawing which illustrates one preferred embodiment of the invention in the form of a longitudinal cross section of a freepiston-type engine with two coaxial piston units adjacent to each other.

The free-piston-type engine according to the invention consists of two piston units, each of which comprises an air-compressor piston 11 or 12 which has a combustion piston 13 and 14 or 15 and 16, respectively, integrally connected thereto at each side thereof. The compression cylinders 17 and 18 are provided with intake slots 19 and 20, respectively, through which the air is drawn in by means of the vacuum produced by the air-compressor pis ton 11 or 12, respectively. When carrying out their outwardly directed strokes, the double-acting air-compressor pistons 11 and 12 supply compressed air through the two conduits 21 and 22 into the common combustion chamber 23 containing the two central combustion pistons 14 and 16, while during their inwardly directed strokes, aircompressor pistons 11 and 12 supply compressed air through conduits 24 and 25 into combustion chambers 26 and 27.

The two outer combustion pistons 13 and 14 operate according to the reverse-scavenging method, for which purpose the combustion chambers 26 and 27 are provided with exhaust slots 28 and 29 and intake slots 30 and 31, respectively. The two inner pistons 14 and 16, however,

, anemone which are made of a smaller diameter than the two outer pistons 13 and 15, operate according to the uniflow-scavenging method, and the common combustion chamber 23 is therefore provided with one intake opening 32 and one exhaust opening 33. For regulating the amount of combustion air drawn into each air-compressor cylinder 17 and 18, the intake pipes 34 and 35 thereof are provided with throttle valves 36 and 37.

Although my invention has been illustrated and described with reference to the preferred embodiment thereof, I wish to have it understood that it is in no way limited to the details of such embodiment, but is capable of numerous modifications within the scope or" the appended claims.

Having thus fully disclosed my invention, what vI claim is:

1. In a free-piston-type engine having at least two co- .axial, double-acting air-compressor pistons disposed in the longitudinal direction of the engine and a combustion piston on each side of each compressor piston and integrally connected thereto was to form a unit, each of said units being adapted to operate in the opposite direction to the other unit, said combustion pistons of both units facing inwardly toward each other being disposed within a common central combustion chamber and being adapted to operate according to the uniflow-scavenging method, each 'ofsaid combustion pistons of both units facing outwardly being disposed within an outer combustion chamber and adapted to operate according to the reverse-scavenging method, the sides of said compressor pistons facing toward said .outer combustion pistons being adapted to .supply compressed air to said common central combustion chamber, the sides of said compressor pistons facing toward said inner combustion pistons being adapted to supply compressed air to said two outer combustion chambers.

2. A free-piston-type engine as defined in claim .1, wherein said inner combustion pistons have a diameter smaller than said two outer combustion pistons.

each of said piston assemblies being adapted to operate in mutually opposite directions, the combustion pistons of both piston assemblies, which face inwardly toward each other and represent the inner combustion pistons, being disposed within the inner portion of said cylinder means to thereby form a common central combustion chamber therebetween, inlet and outlet means provided in said inner cylinder portion for operation of said inner combustion pistons according to the uniflow scavenging method, each of said combustion pistons of both piston assemblies, which face outwardly and represent the outer combustion pistons, being disposed within one of the outer portions of said cylinder means and forming an outer combustion chamber inlet and outlet means provided in each of said outer cylinder portions for operation of said outer combustion pistons according to the loop-scavenging method, each of the cylinder means for said air compressor pistons being provided with inlet and outlet means, conduit means connecting the outlet means of each of said compressor cylinder means on the side of said compressor pistons facing toward said outer combustion pistons with said common central combustion chamber for supplying compressed air thereto, and conduit means connecting the outlet means of each of said compressor cylinder means on the side of said compressor pistons facing toward said inner combustion pistons with a respective one of said outer combustion chambers for supplying compressed air thereto.

4. A free-piston-type engine according to claim 3, wherein said inner combustion pistons have a diameter smaller than said two other combustion pistons.

S. ,A free-piston-type engine according to claim '3, wherein the inlet means in each compressor cylinder means are formed by intake slots located in approximately the longitudinal center of said air compressor cylinder means throughwhich the air is drawn in by means of a vacuum producedbymovement of said air compres- .sor piston.

6. A free-piston-type engine according ,to claim '3, further comprising conduit means connected to the intake means in said air compressor cylinder means and throttle 2,388,756 Meyers Nov. 13, 1945 FOREIGN PATENTS 1,012,777 Germany July 25, 1957 i 

